Method for CAGD recovery of heavy oil

ABSTRACT

The invention provides a novel method of recovering oil by injecting oxygen into a chamber within an oil deposit thereby combusting oil at the chamber walls. The heated oil to drains towards the reservoir floor and is recovered oil via a production well.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.60/773,410 filed Feb. 15, 2006.

FIELD OF THE INVENTION

This invention relates to a method for the recovery of heavy oil. Morespecifically, this invention relates to reducing the energy inputsrequired in Steam Assisted Gravity Drainage (SAGD) methods now employedcommercially. This invention also relates to improved methods forin-situ combustion.

BACKGROUND OF THE INVENTION

In-situ combustion of heavy oil is a potentially attractive method ofmobilizing heavy oil for production. No external source of fuel isrequired and temperatures can be high enough for oil upgrading. However,few commercial trials have been successful because of the difficulty incontrolling combustion. An improvement known as Toe to Heel AirInjection (THAI) is one attempt to solve this issue. Another approach toheavy oil production is heating by steam injection. A recentbreak-through is Steam Assisted Gravity Drainage (SAGD). SAGD is nowwidely used to produce heavy oil from oil sands such as are foundthroughout Alberta.

Although heavy oil can be economically produced, little or no upgradingof the oil is achieved. In SAGD, steam is injected into a heavy oildeposit forming an expanding steam chamber avoiding loss of steamthrough cracks. Heated oil drains to a production well located under theinjection well. Both wells are typically horizontal wells. Typically,the amount of steam required to produce a barrel of oil decreases withtime for a period following initial operation. The minimum steamrequirement is usually reached after three or four years of operation.Inasmuch as a major cost of such an operation is the cost of providingthe steam, there is a need to reduce the amount of steam required to anamount below the minimum now achievable.

It is therefore an object of the present invention to provide asignificant reduction in the amount of steam required to produce oil. Itis a prime object of the invention to make possible utilization ofin-situ combustion to replace at least a portion of the steam requiredin SAGD production of heavy oil from oil sands. Further it is an objectof the invention to provide a method to produce upgraded oil.

SUMMARY OF THE INVENTION

It has now been found that injection of oxygen along with steam into aSAGD steam chamber reduces the amount of steam required to produce abarrel of oil. The resulting in-situ combustion, referred to herein asCombustion Assisted Gravity Drainage (“CAGD”) provides heat to reducethe amount of steam required to produce a barrel of oil and provides fortemperatures high enough for oil upgrading.

In-situ combustion in the presence of steam allows control of reactiontemperature by control of the oxygen concentration in the gases withinthe steam chamber. Temperatures at the chamber wall may be well abovethe saturated steam temperature at the pressure within the chamber. Oilmay be upgraded by cracking and high enough temperatures for steamreaction with carbon or hydrocarbons to produce hydrogen are achievable.For existing SAGD operations, oxygen may be mixed with the steam beinginjected via an injection well. A separate oxygen injection well may beused to inject the oxygen at a higher elevation than the existing steaminjection well.

Injecting oxygen into a SADG steam chamber for in-situ combustionwithout a continuing supply of steam eliminates the need for a surfacefuel supply to produce steam. In this case, air or oxygen-enriched airmay be utilized rather than high purity oxygen. For the purpose of thisinvention, a chamber is a region within a heavy oil deposit bounded bylow permeability walls. A steam chamber is a chamber in an oil reservoirformed by injecting steam into the reservoir replacing all or a portionof the chamber oil with steam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a SAGD steam chamber in a heavy oil deposit operated inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a SAGD steam chamber 30 in heavy oil deposit 40 operatedin accordance with the present invention. As in SAGD, drained oil iswithdrawn through production well 33. Oxygen in admixture with steam isinjected via well 34 to maximize upgrading of produced oil.Alternatively, oxygen in admixture with steam is injected via optionalwell 31 into an upper region of chamber 30. In this mode of operation,oxidation and upgrading of oil draining toward production well 33 may belimited by injection of oxygen-free or reduced-oxygen content fluid, asfor example steam, via well 34 in sufficient quantity to limit access ofoxygen to drained oil being withdrawn through well 33.

Although the present invention has been described in detail withreference to certain preferred versions thereof, other versions arepossible. Therefore, the spirit and scope of the invention should not belimited to the description of the preferred versions contained herein.

1. A method of recovering oil comprising: a) injecting oxygen into achamber within an oil deposit thereby combusting oil at the chamberwalls; b) allowing heated oil to drain towards the reservoir floor; andc) recovering oil via a production well.
 2. The method of claim 1wherein the chamber is a steam chamber.
 3. The method of claim 2 whereinthe combustion temperature at the chamber walls is above the saturatedsteam temperature at the steam chamber pressure.
 4. The method of claim2 wherein the combustion temperature is controlled by adjusting theoxygen concentration within the steam chamber.
 5. The method of claim 1wherein the oxygen is injected in admixture with steam.
 6. The method ofclaim 5 wherein high purity oxygen is injected in admixture with steam.7. The method of claim 1 wherein the chamber walls are maintained at atemperature above that at which the in place oil cracks.
 8. The methodof claim 5 wherein the combustion temperature is high enough to promotereaction of steam with carbonaceous materials.
 9. A method of producingupgraded oil from a heavy oil deposit comprising: a) injecting oxygeninto a chamber within the deposit; b) combusting fuel at the chamberwalls; c) maintaining the walls at a temperature above that at which thedeposit oil cracks; and d) withdrawing upgraded oil via a productionwell.
 10. The method of claim 9 wherein the oxygen is injected inadmixture with steam.
 11. The method of claim 9 wherein the oxygen isinjected in admixture with nitrogen.
 12. The method of claim 1 whereinoxygen is supplied as air.